Switched Reluctance Machine Phase Winding Discharge Control
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Solution Overview
Problem
Existing methods for discharging additional energy storage devices in hybrid and electric vehicles, such as ultracapacitors, are either costly, increase component complexity, or fail to efficiently lower the state of charge to a predetermined shutdown voltage, potentially harming the energy store's service life.
Innovation Solution
Employing a switched reluctance machine as a discharge resistor, utilizing its phase inductance when stationary to safely and cost-effectively discharge the energy store by controlling the phase windings with an inverter to avoid torque generation and distribute heat loss, thereby avoiding unwanted movement and excessive heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an additional discharge resistor is provided and activated by a switch, then the energy store can be discharged to a predetermined shutdown voltage, but additional components are required causing increased space requirement and costs
Solution Approach 1:
The patent applies multi-functionality by enabling the phase windings of the reluctance machine to serve dual purposes: driving the vehicle motor and discharging the energy store. The control unit switches the phase windings between motor operation mode and discharge mode based on operational requirements, eliminating the need for separate discharge resistors and switches.
2Reliability
If symmetry resistors or circuits are used to compensate for differences between individual cells, then cell balance is improved, but the thermal dimensioning and power dimensioning are not suitable for discharging the entire energy store within an appropriate time window
Solution Approach 1:
The patent applies dynamics by making the discharge capability adjustable and controllable. The control unit can dynamically adjust the discharge current through the phase windings based on the required discharge rate and thermal conditions. This allows the system to discharge the entire energy store within an appropriate time window while managing thermal loads, unlike fixed dimensioning of symmetry resistors.
3Reliability
If the conventional 12 V or 24 V battery is used to absorb energy from the additional energy store via the DC/DC converter, then discharge is possible, but the conventional battery also has a high state of charge and cannot absorb the released energy
Solution Approach 1:
The patent uses the phase windings of the reluctance machine as an intermediary discharge path. Instead of directly transferring energy between batteries, the system uses the reluctance machine's phase windings (controlled by the inverter) as a mediator to dissipate or store the energy from the additional energy store, bypassing the limitation of the conventional battery's charge state.
4Productivity
If phase windings are energized to discharge the energy store, then discharge current flows, but torque is generated causing unwanted vehicle movement
Solution Approach 1:
The patent applies local quality by selectively energizing specific phase windings based on the rotor position to achieve discharge while minimizing torque. The control unit monitors rotor position and activates only those phase windings that produce minimal or zero torque at the current rotor angle, allowing discharge current to flow without causing unwanted vehicle movement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides a cost-effective and reliable means to discharge the energy store to a predetermined shutdown state, extending the service life of the energy storage devices and reducing component complexity and costs.
Implementation Method 1
at least one phase winding is energized as a discharge resistor by means of the inverter, in which a magnetic field generated by a discharge current does not develop any force or torque that is large enough to move the drive train or the motor vehicle
Data Source
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AI summary
The invention relates to a method for discharging an electrical energy storage device intended to supply an electric motor of a motor vehicle. The invention particularly relates to such a method for discharging the electrical energy storage device to a predetermined shutdown voltage. According to general principles of the invention, the electric motor is a switched reluctance machine whose phase windings (U, V, W) are controlled by an inverter using switches.The method provides that, after fulfillment of at least one activation condition (S2) to activate a discharge process of the energy storage device, the discharge process is activated, in which the energy storage device is discharged to a predetermined shutdown state via the reluctance machine, whereby at least one phase winding is energized as a discharge resistor by means of the inverter, in which a magnetic field generated by a discharge current does not develop a force large enough to move the drive train or the motor vehicle (S3, S4).